Glass-Free Microwave Dielectric Ceramics and the Manufacturing Method Thereof

ABSTRACT

A glass-free microwave dielectric ceramic that can be sintered at low temperature, and a manufacturing method thereof are provided. The glass-free microwave dielectric ceramic composition includes a composition represented by a formula, M 2+ N 4+ B 2 O 6 , wherein M is one element of Ba, Ca and Sr, and N is one element of Sn, Zr and Ti. The M may be replaced by two elements of Ba, Ca and Sr different from each other, to form a composition represented by a formula, (M 1-x   2+ M x   2+ )N 4+ B 2 O 6 , wherein 0&lt;x&lt;1. The N may also be replaced by two elements of Sn, Zr and Ti different from each other, to form a composition represented by a formula, M 2+ (N 1-y   4+ N y   4+ )B 2 O 6 , wherein 0&lt;y&lt;1. Furthermore, it is also possible to replace both of the M and N to form a composition represented by a formula, (M 1-x   2+ M x   2+ )(N 1-y   4+ N y   4+ )B 2 O 6 , wherein 0&lt;x&lt;1 and 0&lt;y&lt;1. In addition, the glass-free microwave dielectric ceramic composition may further includes 1 wt % to 7 wt % of a sintering agent represented by a formula, βCuO+γBi 2 O 3 , wherein 0.55&lt;β&lt;0.96 and 0.40&lt;γ≦0.45. As such, the glass-free microwave dielectric ceramic composition may be sintered at a low temperature at lowest 875° C.

TECHNICAL FIELD

The present disclosure relates to a microwave dielectric ceramics and amanufacturing method thereof, and more particularly, to a glass-freemicrowave dielectric ceramics which can be sintered together with aninternal conductor and has superior microwave dielectriccharacteristics, and a manufacturing method thereof.

BACKGROUND ART

Recently, as a market for mobile communication terminals, such as amobile phone and a personal digital assistant (PDA), and Bluetoothproducts for facilitating ubiquitous communications is growing rapidly,high-frequency devices constituting them, such as a microwave filter, aduplexer, a resonator, and an integrated circuit board are required tobecome smaller and lighter, and to be stacked and surface-mounted.

Such high-frequency devices include dielectric ceramic materials. Thedielectric ceramics for the high-frequency devices should have specificdielectric characteristics as follows.

First, in order to reduce the device size, the dielectric ceramicsshould have a high dielectric constant, ∈_(r). This is because awavelength of the microwave in the dielectric ceramics is decreased ininverse proportion to the square root of the dielectric constant.However, a microwave transmission line provided to a board of radiofrequency (RF)/microwave module should rather have a low dielectricconstant so as to increase the speed.

Second, for a highly efficient operation, the dielectric ceramics shouldhave a high quality factor (Q) within an operation frequency range. Inother words, the dielectric ceramics should have a low dielectric loss,tan δ, which is a reciprocal of the quality factor. In general, thequality factor is evaluated based on the product of the quality factorand a corresponding resonance frequency, Q×f, or the dielectric loss, areciprocal of the quality factor.

Third, for an accurate operation of the operation frequency, thedielectric ceramics should have a temperature coefficient factor (TCF)of the resonance frequency, τ_(f), close to zero.

Meanwhile, a method for stacking high-frequency devices underdevelopment in recent times includes printing a conductive pattern on agreen sheet of dielectric ceramics, stacking the printed green sheets,and then sintering them. This method allows lots of elements such as aninductor, a capacitor and a resistor to be integrated in a single modulewithout additional lead wire. Accordingly, the package size can bereduced significantly.

However, the method requires that an internal conductor formed of silver(Ag) or copper (Cu) having excellent conductivity should be sinteredtogether with the dielectric ceramics. Accordingly, a low temperatureco-fired ceramics (LTCC) is demanded strongly. The LTCC can be sinteredat a temperature lower than approximately 950° C., however, has a highquality factor and a low resonance frequency. However, most of therecently developed LTCC suffers from significantly deterioratedmicrowave dielectric characteristics, such as insufficientdensification, low dielectric constant clue to the addition of sinteringagents, lowered quality factor, increased temperature coefficient factorof the resonance frequency, and the like.

Furthermore, the typical LTCC is formed of ceramic materials having acomposite structure including a glass matrix and an alumina (Al₂O₃)powder filler mixed thereto. However, this typical LTCC is reported tosuffer from difficulty in controlling rheology during the ceramic slurryformation, ununiform glass composition, ununiform dispersion, and thelike. Consequently, a glass-free (or non-glass) LTCC compositionincluding no glass or minimum amount of glass is attracting considerableinterests.

DISCLOSURE Technical Problem

Accordingly, the present disclosure provides a glass-free microwavedielectric ceramics having superior microwave dielectriccharacteristics, and a manufacturing method thereof.

The present disclosure also provides a low temperature co-firedmicrowave dielectric ceramics that can be sintered at low temperature byadding a low temperature sintering agent to the glass-free microwavedielectric ceramics, and a manufacturing method thereof.

Technical Solution

Embodiments provide a microwave dielectric ceramics includes M²⁺N⁴⁺B₂O₆component, where M may be substituted for by two different divalentmetals and/or N may be substituted for by two different tetravalentmetals.

ADVANTAGEOUS EFFECTS

A microwave dielectric ceramic in accordance with an exemplaryembodiment includes M²⁺N⁴⁺B₂O₆ composition. Here, M may be replaced bytwo divalent metals different from each other and/or N may be replacedby two tetravalent metals different from each other. As such, themicrowave dielectric ceramic can have superior microwave dielectriccharacteristics without a glass matrix, and thus can be advantageouslyapplied to a high-frequency device.

In addition, by adding Bi₂O₃—CuO based sintering agent to the microwavedielectric ceramic composition, the microwave dielectric ceramic can besintered at low temperature without deterioration of dielectriccharacteristics. Accordingly, the microwave dielectric ceramic can beadvantageously applied to a low temperature co-firing ceramic device,which has superior microwave dielectric characteristics.

DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating microwave dielectric characteristics ofBaZr(MO₃)₂ ceramic in accordance with an exemplary embodiment.

FIG. 2 is a scanning electron microscope (SEM) image of the BaZr(MO₃)₂ceramic of FIG. 1.

FIG. 3 is a SEM image of Ba(Zr_(1-x)Ti_(x))B₂O₆ ceramic sintered for 2hours at 1,050° C. in accordance with another exemplary embodiment.

FIG. 4 is a SEM image of BaZr(BO₃)₂ ceramic added with 5 wt % of0.88Bi₂O₃-0.12CuO as a sintering agent, and sintered for 2 hours at 900°C. in accordance with further another exemplary embodiment.

BEST MODE

In accordance with an exemplary embodiment, a glass-free microwavedielectric ceramic composition includes a composition represented by aformula, M²⁺N⁴⁺B₂O₆, wherein M is one element of Ba, Ca and Sr, and N isone element of Sn, Zr and Ti.

The M may be replaced by two elements of Ba, Ca and Sr different fromeach other, to form a composition represented by a formula, (M_(1-x)²⁺M_(x) ²⁺)N⁴⁺B₂O₆, wherein 0<x<1. The N may also be replaced by twoelements of Sn, Zr and Ti different from each other, to form acomposition represented by a formula, M²⁺(N_(1-y) ⁴⁺N_(y) ⁴⁺)B₂O₆,wherein 0<y<1. Furthermore, it is also possible that the M is replacedby two elements of Ba, Ca and Sr different from each other, and the N isreplaced by two elements of Sn, Zr and Ti different from each other, toform a composition represented by a formula, (M_(1-x) ²⁺M_(x)²⁺)(N_(1-y) ⁴⁺N_(y) ⁴⁺)B₂O₆, wherein 0<x<1 and 0<y<1.

In addition, the glass-free microwave dielectric ceramic composition mayfurther includes a sintering agent represented by a formula,βCuO+γBi₂O₃, wherein β is from 0.55 to 0.96, and γ is from 0.40 to 0.45.The concentration of the sintering agent in the dielectric ceramiccomposition may be from 1 wt % to 7 wt %.

In accordance with another exemplary embodiment, a method formanufacturing a glass-free microwave dielectric ceramic materialincludes: mixing and pulverizing one of the above described dielectricceramic composition; drying and calcinating the mixed and pulverizeddielectric ceramic composition; mixing and pulverizing the dried andcalcinated dielectric ceramic composition with a sintering agentrepresented by a formula, βCuO+γBi₂O₃, to obtain a sample, wherein β isfrom 0.55 to 0.96, and γ is from 0.40 to 0.45, and drying the sample;molding and sintering the molded sample. The sintering agent may beadded in the range of from 1 wt % to 7 wt %. The sintering of the moldedsample may be performed at from 875° C. to 1,000° C. As such, theglass-free microwave dielectric ceramic material can be sintered at lowtemperature without significant deterioration of microwave dielectriccharacteristics.

MODE FOR INVENTION

A microwave dielectric ceramic in accordance with an exemplaryembodiment has a ceramic composition represented by the formula 1:

M²⁺N⁴⁺B₂O₆  (1),

where M is a divalent metal element such as Ba, Ca, Sr, and the like,and N is a tetravalent metal element such as Sn, Zr, Ti, and the like.The inventors found that the microwave dielectric ceramic has a dolomitestructure and an anisotropic thermal expansion characteristic.

Also, the formula 1 may be modified by replacing the metal element M orN by two metal elements different from each other. That is, the formula1 may be modified in such a manner that the metal element M is replacedby two divalent metal elements different from each other, and/or themetal element N is replaced by two tetravalent metal elements differentfrom each other. In this case, the formula 1 of the microwave dielectricceramic may be modified into one of the following formulas:

(M_(1-x) ²⁺M_(x) ²⁺)N⁴⁺B₂O₆  (2),

M²⁺(N_(1-y) ⁴⁺N_(y) ⁴⁺)B₂O₆  (3),

(M_(1-x) ²⁺M_(x) ²⁺)(N_(1-y) ⁴⁺N_(y) ⁴⁺)B₂O₆  (4),

where 0<x<1 and 0<y<1. The two M's may be any divalent metal elements,such as Ba, Ca, Sr, and the like, which are different from each other.The two N's may be any tetravalent metal elements, such as Sn, Zr, Ti,and the like, which are different from each other.

The inventors found that sintering temperatures of the microwavedielectric ceramics of formulas 1 to 4 are higher than approximately1,100° C.

Such a high sintering temperature makes the ceramics difficult to beapplied to LTCC. Therefore, according to the other desirable embodimentof the present invention, in order to lower the sintering temperature, asintering agent including CuO and Bi₂O₃ for a low temperature sinteringis added to the composition of the microwave dielectric ceramics havingthe formulas 1 to 4. The sintering agent can be represented by thefollowing formula:

α wt %(βCuO+γBi₂O₃)  (5),

where 1≦α≦7, 0.55≦β≦0.96, and 0.40≦γ≦0.45.

In summary, the microwave dielectric ceramics of the formulas 1 to 4 aredifficult to be used for the LTCC because they have sinteringtemperatures higher than approximately 1,100° C. However, as a sinteringagent including CuO and Bi₂O₃ having a eutectic point of approximately600±20° C. is added to the microwave dielectric ceramics, the sinteringtemperature can be lowered preferably to between 875° C. and 1,000° C.,more preferably to between 875° C. and 925° C., further more preferablyto 875° C. During the sintering process, the CuO and Bi₂O₃ form a liquidphase in an internal interface of the ceramic to acceleratedensification of the ceramic. Consequently, the microwave dielectricceramic can be sintered at a low temperature with superior microwavedielectric characteristics.

Hereinafter, specific embodiments will be described in detail withreference to the accompanying drawings. The invention may, however, beembodied in many different forms and should not be construed as beinglimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the concept of the invention to those skilled in theart.

Examples 1 to 5

In these examples, BaZr(BO₃)₂ ceramics consisting essentially of thecomposition of the formula 1 were prepared and sintered at varioussintering temperatures, and microwave dielectric characteristics thereofwere measured.

In specific, reagents BaCO₃, ZrO₂, and B₂O₃ or H₃BO₃ were weighed toform the composition of BaZr(BO₃)₂. The weighed reagents were mixed andpulverized with zirconia balls for 24 hours using deionized water as adispersion solvent. The mixed and pulverized sample was dried, and thencalcinated for 4 hours at between 900° C. and 1,150° C. to synthesize asolid solution of a dolomite structure (hexagonal symmetry). Thesynthesized powder was pulverized again for 24 hours with a wet ballmill to form a fine powder having an average particle diameter ofapproximately 1 μm. The fine powder was added with 2 wt % of polyvinylalcohol (PVA) binder aqueous solution, and pressed into a cylinder shapeof 10 mm diameter and 5 mm to 6 mm thickness, at 1 ton/cm². The sampleof a cylinder shape was heat-treated for 1 hour at 400° C. to remove abinder, and then sintered for 2 hours at a temperature between 1,100° C.and 1,300° C. Both edges of the sintered sample were ground with SiCabrasive paper. Then, dielectric constant (∈_(r)) at 1 MHz, dielectricloss (tan δ), and temperature coefficient of capacitance (TCC) wasmeasured by an impedance analyzer (4294A, Agilent Technologies Inc.,USA). Here, the TCC was measured at a temperature range from −25° C. to125° C. Also, dielectric characteristics in a microwave region weremeasured by a network analyzer (8720ES, Agilent Technologies Inc., USA)with a post resonator method and a cavity resonator method. Here, thetemperature coefficient of resonant frequency (τ_(f)) was measured at atemperature range from 25° C. to 80° C.

The microwave dielectric characteristics of the samples according to thesintering temperature ranging from 1,100° C. to 1,300° C. are shown inTable 1 and FIG. 1.

TABLE 1 Temperature Sintering Dielectric Quality coefficient temperatureFrequency constant factor (τ_(f): ppm/ Example (° C.) (GHz) (ε_(r)) (Q)° C.) 1 1,100 15.3276 11.16 902 −0.3 2 1,150 15.0991 10.71 1,003 −6.1 31,200 7.4247 11.25 2,073 −13.7 4 1,250 13.0001 11.99 587 −2.1 5 1,30013.0600 11.82 652 −1.4

Referring to Table 1 and FIG. 1, the BaZr(BO₃)₂ ceramic sintered at1,100° C. shows a quality factor of approximately 900 at a frequency of15 GHz and a dielectric constant of approximately 11. Example 3 sinteredfor 2 hours at 1,200° C. shows the highest quality factor of 2,073 amongthe above-listed examples. FIG. 2 shows a SEM image of Example 3.

On the contrary, Examples 4 and 5 shows significantly reduced qualityfactors as the sintering temperature increases above 1,250° C. This isprobably because BaZr(BO₃)₂ phase is decomposed to generate BaZrO₃phase.

Examples 6 to 9

In these examples, CaZr(BO₃)₂ ceramics consisting essentially of thecomposition of the formula 1 were prepared and microwave dielectriccharacteristics thereof according to respective sintering temperatureswere measured. CaCO₃, ZrO₂, and B₂O₃ or H₃BO₃ were used as startingmaterials. Sample preparation and measurement procedures wereessentially identical to those described in Examples 1 to 5 except thesintering temperature. In these examples, samples were sintered for 2hours at a temperature from 1,000° C. to 1,150° C.

The microwave dielectric characteristics of the CaZr(BO₃)₂ ceramicsprepared and measured according to these examples are shown in Table 2.

TABLE 2 Temperature Sintering Dielectric Quality coefficient temperatureFrequency constant factor (τ_(f): ppm/ Example (° C.) (GHz) (ε_(r)) (Q)° C.) 6 1,000 16.5118 — 1,555 — 7 1,050 16.3868 — 1,873 — 8 1,10016.1439 7.4 1,914 −9.6 9 1,150 16.2759 — 1,761 —

Examples 10 to 13

In these examples, SrZr(BO₃)₂ ceramics consisting essentially of thecomposition of the formula 1 were prepared and microwave dielectriccharacteristics thereof according to respective sintering temperatureswere measured. SrCO₃, ZrO₂, and B₂O₃ or H₃BO₃ were used as startingmaterials. Sample preparation and measurement procedures wereessentially identical to those described in Examples 6 to 9.

The microwave dielectric characteristics of the SrZr(BO₃)₂ ceramicsprepared and measured according to these examples are shown in Table 3.

TABLE 3 Temperature Sintering Dielectric Quality coefficient temperatureFrequency constant factor (τ_(f): ppm/ Example (° C.) (GHz) (ε_(r)) (Q)° C.) 10 1,000 16.5607 — 1,002 — 11 1,050 16.3841 — 1,275 — 12 1,10016.1126 7.0 2,074 −9.1 13 1,150 15.8069 — 933 —

Examples 14 to 17

In these examples, SrSn(BO₃)₂ ceramics consisting essentially of thecomposition of the formula 1 were manufactured and microwave dielectriccharacteristics thereof according to respective sintering temperatureswere measured. SrCO₃, SnO₂, and B₂O₃ or H₃BO₃ were used as startingmaterials. Sample preparation and measurement procedures wereessentially identical to those described in Examples 6 to 9.

The microwave dielectric characteristics of the SrSn(BO₃)₂ ceramicsprepared and measured according to these examples are shown in Table 4.

TABLE 4 Temperature Sintering Dielectric Quality coefficient temperatureFrequency constant factor (τ_(f): ppm/ Example (° C.) (GHz) (ε_(r)) (Q)° C.) 14 1,000 17.2340 — 665 — 15 1,050 16.6507 — 1,030 — 16 1,10016.1751 7.1 1,150 −3.9 17 1,150 15.8567 — 960 —

Examples 18 to 21

In these examples, CaSn(BO₃)₂ ceramics consisting essentially of thecomposition of the formula 1 were prepared and microwave dielectriccharacteristics thereof according to respective sintering temperatureswere measured. CaCO₃, SnO₂, and B₂O₃ or H₃BO₃ were used as startingmaterials. Sample preparation and measurement procedures wereessentially identical to those described in Examples 6 to 9.

The microwave dielectric characteristics of the CaSn(BO₃)₂ ceramicsprepared and measured according to these examples are shown in Table 5.

TABLE 5 Temperature Sintering Dielectric Quality coefficient temperatureFrequency constant factor (τ_(f): ppm/ Example (° C.) (GHz) (ε_(r)) (Q)° C.) 18 1,000 17.7197 — 480 — 19 1,050 17.4157 — 567 — 20 1,100 17.25905.6 790 −4.6 21 1,150 16.9775 — 640 —

Examples 22 to 29

In these examples, Ba(Zr_(1-x)Ti_(x))B₂O₆ (where 0<x<1) ceramicsconsisting essentially of the composition of the formula 3 were preparedand microwave dielectric characteristics thereof according to respectivesintering temperatures were measured. BaCO₃, ZrO₂, TiO₂, and B₂O₃ orH₃BO₃ were used as starting materials. Sample preparation andmeasurement procedures were essentially identical to those described inExamples 6 to 9.

The microwave dielectric characteristics of the Ba(Zr,Ti)B₂O₆ ceramicsaccording to respective mole fractions of Zr/Ti and respective sinteringtemperatures are shown in Table 6. A SEM image of Example 22 sinteredfor 2 hours at 1,050° C. is shown in FIG. 3.

TABLE 6 Com- Sintering Di- Temperature Ex- posi- temper- electricQuality coefficient am- tion ature Frequency constant factor (τ_(f):ppm/ ple (Zr/Ti) (° C.) (GHz) (ε_(r)) (Q) ° C.) 22 1/1 1,050 11.926112.82 2,250 −31 23 1/1 1,100 12.1784 12.00 690 −23 24 1/1 1,150 12.425211.28 366 −46 25 1/3 1,075 7.0213 12.14 978 — 26 3/1 1,100 7.2338 12.061,676 —

In addition, low frequency dielectric characteristics of Examples 22 to24 of Ba(Zr_(1/2)Ti_(1/2))B₂O₆ ceramics sintered at 1,050° C., 1,100° C.and 1,150° C., respectively, were measured. These are shown in Table 7,as Examples 27 to 29.

TABLE 7 Di- Di- Temperature Ex- Sintering electric electric cefficientam- temperature Frequency constant loss (τ_(f): ppm/ ple (° C.) (MHz)(ε_(r)) (tan δ) ° C.) 27 1,050 1 12.66  1.8 × 10⁻⁴ — 28 1,100 1 12.05  8 × 10⁻⁴ — 29 1,150 1 11.96 13.3 × 10⁻⁴ —

Examples 30 to 33

In these examples, Ba(Sn_(1-x)Zr_(x))B₂O₆ (where 0<x<1) ceramicsconsisting essentially of the composition of the formula 3 were preparedand microwave dielectric characteristics thereof according to respectivesintering temperatures were measured. BaCO₃, SnO₂, ZrO₂, and B₂O₃ orH₃BO₃ were used as starting materials. Sample preparation andmeasurement procedures were essentially identical to those described inExamples 6 to 9.

The microwave dielectric characteristics of the Ba(Sn,Zr)B₂O₆ ceramicsaccording to respective mole fractions of Sn/Zr and respective sinteringtemperatures are shown in Table 8.

TABLE 8 Com- Sintering Di- Temperature Ex- posi- temper- electricQuality coefficient am- tion ature Frequency constant factor (τ_(f):ppm/ ple (Sn/Zr) (° C.) (GHz) (ε_(r)) (Q) ° C.) 30 1/3 1,100 8.1937 9.33173 — 31 1/1 1,100 13.9786 9.74 1,072 — 32 1/1 1,150 13.7750 10.24 1,215— 33 3/1 1,100 8.2366 9.48 1,094 —

Examples 34 to 37

In these examples, a low temperature sintering agent including CuO andBi₂O₃ was added to BaZr(BO₃)₂ ceramics of Examples 1 to 5 in order tomanufacture ceramic materials that can be sintered at a low temperaturebelow 1,000° C.

In specific, reagents CuO and Bi₂O₃ were weighed to form a sinteringagent having the composition of formula 5, (βCuO+γBi₂O₃), where β=0.12and γ=0.88. Then, the BaZr(BO₃)₂ powders calcinated and synthesized asdescribed in Examples 1 to 5 were added with from 1 wt % to 7 wt % ofthe sintering agents having the composition of 0.12CuO+0.88Bi₂O₃.Thereafter, sample preparation and measurement procedures are performed,which are identical to those of Examples 1 to 5 after the calcination.However, the sintering conditions were not identical to those ofExamples 1 to 5. Instead, the sintering was performed for 2 hours at atemperature from 875° C. to 925° C. Table 9 shows microwave dielectriccharacteristics of the BaZr(BO₃)₂ ceramics added with 5 wt % of thesintering agents having the composition of 0.12CuO+0.88Bi₂O₃. FIG. 4shows a SEM image thereof when sintering was performed for 2 hours at900° C.

TABLE 9 Dielectric loss (tan δ) Sintering Dielectric or Temperaturetemperature constant Quality coefficient Measurement Example Frequency(° C.) (ε_(r)) factor (Q) (ppm/° C.) method 34  1 MHz 875 11.35 3 × 10⁻⁵— Impedance (tan δ) analyzer 35  1 MHz 900 11.50 7 × 10⁻⁵ — (tan δ) 36 1 MHz 925 11.51 1 × 10⁻⁵ — (tan δ) 37 16 GHz 900 11.80 880 +1.1 Network(Q) analyzer

Referring to Table 9 and FIG. 4, the BaZr(BO₃)₂ ceramic that is addedwith 5 wt % of the sintering agent having the composition of0.12CuO+0.88Bi₂O₃ and sintered for 2 hours at 900° C. shows a dielectricconstant of 11.8, a quality factor of 880, and a temperature coefficientof approximately 1 ppm/° C. Accordingly, the ceramic shows superiormicrowave dielectric characteristics although the sintering temperatureis lowered to 900° C.

Examples 38 to 43

In these examples, BaSnB₂O₆, CaZrB₂O₆, SrZrB₂O₆, BaZrB₂O₆, CaSnB₂O₆, andSrSnB₂O₆ ceramics consisting essentially of the composition of theformula 1 were prepared and microwave dielectric characteristics thereofaccording to respective sintering temperatures were measured. Samplepreparation and measurement procedures were essentially identical tothose described in Examples 1 to 5 except the sintering temperature. Thesintering temperature was fixed to 1,100° C.

In addition, BaSnB₂O₆, CaZrB₂O₆, SrZrB₂O₆, BaZrB₂O₆, CaSnB₂O₆, andSrSnB₂O₆ ceramic powders calcinated and synthesized as described inExamples 1 to 5 were prepared. Then, the ceramic powders were added with5% of sintering agents having the composition of 0.12CuO+0.88Bi₂O₃, andsintered at 900° C., respectively. Other procedures were essentiallyidentical to those described in Examples 1 to 5.

The microwave dielectric characteristics of the samples prepared andmeasured as described above are shown and compared in Table 10. In Table10, BC refers to the sintering agent having the composition of0.12CuO+0.88Bi₂O₆.

TABLE 10 Microwave dielectric characteristics Quality factor (Q)(Frequency: 16 GHz) Di- 5 wt % Temperature Ex- electric Without BC BCadded coefficient am- constant (sintering (sintering (τ_(f): ppm/ pleComposition (ε_(r)) at 1,100° C.) at 900° C.) ° C.) 38 BaSnB₂O₆ 9.8 850350 −45 39 CaZrB₂O₆ 7.4 1,910 1,880 −9.6 40 SrZrB₂O₆ 7.0 2,070 1,390−9.1 41 BaZrB₂O₆ 11.6 1,200 902 −0.3 42 CaSnB₂O₆ 5.6 790 1,560 −4.6 43SrSnB₂O₆ 7.1 1,150 1,310 −3.9

Examples 44 to 46

In these examples, (Ba_(1-x)Ca_(x))ZrB₂O₆ (where 0<x<1) ceramicsconsisting essentially of the composition of the formula 2 were preparedand microwave dielectric characteristics thereof were measured. BaCO₃,CaCO₃, ZrO₂, and B₂O₃ or H₃BO₃ were used as starting materials. Samplepreparation and measurement procedures were essentially identical tothose described in Examples 6 to 9.

The microwave dielectric characteristics of the (Ba_(1-x)Ca_(x))ZrB₂O₆ceramics according to respective mole fractions of Ba/Ca and respectivesintering temperatures are shown in Table 11.

TABLE 11 Di- Temper- Ex- Compo- Sintering electric Quality ature am-sition temperature constant factor coefficient ple (Ba/Ca) Frequency (°C.) (ε_(r)) (Q) (ppm/° C.) 44 1/1 100 MHz 1,075 11.59 1960 — 45 1/3 100MHz 1,075 13.29 1738 — 46 3/1 100 MHz 1,075 10.17 1670 —

Examples 47

In this example, (Ba_(1-x)Ca_(x))(Zr_(1-y)Ti_(y))B₂O₆ (where 0<x<1,0<y<1) ceramic consisting essentially of the composition of the formula4 was manufactured and microwave dielectric characteristics thereof weremeasured. BaCO₃, CaCO₃, ZrO₂, TiO₂, and B₂O₃ or H₃BO₃ were used asstarting materials. Sample preparation and measurement procedures wereessentially identical to those described in Examples 6 to 9.

The microwave dielectric characteristics of the(Ba_(1-x)Ca_(x))(Zr_(1-y)Ti_(y))B₂O₆ ceramics according to molefractions of Ba/Ca and Zr/Ti and a sintering temperature are shown inTable 12.

TABLE 12 Compo- sition Di- Temper- Ex- (Ba/Ca Sintering electric Qualityature am- and temperature constant factor coefficient ple Zr/Ti)Frequency (° C.) (ε_(r)) (Q) (ppm/° C.) 47 1/1 100 MHz 1,000 13.17 130 —

Examples 48 to 50

In these examples, (Ba_(1-x)Ca_(x))ZrB₂O₆, Ba(Zr_(1-x)Ti_(x))B₂O₆, and(Ba_(1-x)Ca_(x))(Zr_(1-y)Ti_(y))B₂O₆ (where 0<x<1, 0<y<1) ceramicsconsisting essentially of the compositions of the formulas 2 to 4,respectively, were prepared. Then, the ceramics were added with 3 wt %of the sintering agents having the composition of 0.12CuO+0.88Bi₂O₃, andsintered at a temperature from 900° C. to 925° C. The microwavedielectric characteristics of the samples prepared and measured asdescribed above are shown in Table 13.

TABLE 13 Sintering Dielectric Quality Temperature temperature constantfactor coefficient Example Composition Frequency (° C.) (ε_(r)) (Q)(ppm/° C.) 48 (Ba_(1/2)Ca_(1/2))ZrB₂O₆ + 100 MHz 925 14.09 1570 — 3 wt %(0.88Bi₂O₃ + 0.12CuO) 49 Ba(Zr_(1/2)Ti_(1/2))B₂O₆ + 100 MHz 925 15.82320 — 3 wt % (0.88Bi₂O₃ + 0.12CuO) 50(Ba_(1/2)Ca_(1/2))(Zr_(1/2)Ti_(1/2)) 100 MHz 925 17.24 210 — B₂O₆ + 3 wt% (0.88Bi₂O₃ + 0.12CuO)

As described above, the ceramics consisting essentially of thecompositions of the formulas 1 to 4 and added with the Bi₂O₃—CuO basedsintering agent can be sintered at a low temperature ranging from 900°C. to 925° C. without significant deterioration of dielectriccharacteristics. As such, the ceramics in accordance with the exemplaryembodiments of the present invention can be used as an excellentmaterial for a capacitor, a microwave LTCC device and a substrateincluding silver or copper as an internal electrode.

It will be obvious to those skilled in the art that the sinteringtemperature for optimum microwave dielectric characteristics may bevaried slightly, within an acceptable error range, according tocharacteristics of a powder, such as average particle size, distributionand specific surface, purity of a starting material, impurity content,and sintering condition.

Although the glass-free microwave dielectric ceramics and manufacturingmethod thereof have been described with reference to the specificembodiments, they are not limited thereto. Therefore, it will be readilyunderstood by those skilled in the art that various modifications andchanges can be made thereto without departing from the spirit and scopeof the present invention defined by the appended claims.

1. A dielectric ceramic composition, comprising a compositionrepresented by a formula:M²⁺N⁴⁺B₂O₆, wherein M is one element of Ba, Ca and Sr, and N is oneelement of Sn, Zr and Ti.
 2. The dielectric ceramic composition of claim1, wherein the M is replaced by two elements of Ba, Ca and Sr differentfrom each other, to form a composition represented by a formula:(M_(1-x) ²⁺M_(x) ²⁺)N⁴⁺B₂O₆, wherein 0<x<1.
 3. The dielectric ceramiccomposition of claim 1, wherein the N is replaced by two elements of Sn,Zr and Ti different from each other, to form a composition representedby a formula:M²⁺(N_(1-y) ⁴⁺N_(y) ⁴⁺)B₂O₆, wherein 0<y<1.
 4. The dielectric ceramiccomposition of claim 1, wherein the M is replaced by two elements of Ba,Ca and Sr different from each other, and the N is replaced by twoelements of Sn, Zr and Ti different from each other, to form acomposition represented by a formula:M_(1-x) ²⁺M_(x) ²⁺)(N_(1-y) ⁴⁺N_(y) ⁴⁺)B₂O₆, wherein 0<x<1 and 0<y<1. 5.The dielectric ceramic composition of claim 1 further comprising asintering aid including CuO and Bi₂O₃.
 6. The dielectric ceramiccomposition of claim 1 further comprising a sintering aid represented bya formula:βCuO+γBi₂O₃, wherein β is from 0.55 to 0.96, and γ is from 0.40 to 0.45.7. The dielectric ceramic composition of claim 6, wherein aconcentration of the sintering aid in the dielectric ceramic compositionis from 1 wt % to 7 wt %.
 8. A method for manufacturing a microwavedielectric ceramic material, the method comprising: mixing andpulverizing the dielectric ceramic composition of claim 1 drying andcalcinating the mixed and pulverized dielectric ceramic composition;mixing and pulverizing the dried and calcinated dielectric ceramiccomposition with a sintering aid represented by a formula, βCuO+γBi₂O₃,to obtain a sample, wherein β is from 0.55 to 0.96, and γ is from 0.40to 0.45; drying the sample; molding the dried sample; and sintering themolded sample.
 9. The method of claim 8, wherein a concentration of thesintering aid in the sample is from 1 wt % to 7 wt %.
 10. The method ofclaim 8, wherein the sintering of the molded sample is performed at from875° C. to 1,000° C.
 11. The dielectric ceramic composition of claim 2further comprising a sintering aid including CuO and Bi₂O₃.
 12. Thedielectric ceramic composition of claim 3 further comprising a sinteringaid including CuO and Bi₂O₃.
 13. The dielectric ceramic composition ofclaim 4 further comprising a sintering aid including CuO and Bi₂O₃. 14.The dielectric ceramic composition of claim 2 further comprising asintering aid represented by a formula:βCuO+γBi₂O₃, wherein β is from 0.55 to 0.96, and γ is from 0.40 to 0.45.15. The dielectric ceramic composition of claim 3 further comprising asintering aid represented by a formula:βCuO+γBi₂O₃, wherein β is from 0.55 to 0.96, and γ is from 0.40 to 0.45.16. The dielectric ceramic composition of claim 4 further comprising asintering aid represented by a formula:βCuO+γBi₂O₃, wherein β is from 0.55 to 0.96, and γ is from 0.40 to 0.45.